1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161

use super::constants::*;
use crate::growth::growth_trait::{Growth, GrowthWithConstantTimeAccess};
use crate::{Fragment, SplitVec};

/// Strategy which allows creates a fragment with double the capacity
/// of the prior fragment every time the split vector needs to expand.
///
/// Assuming it is the common case compared to empty vector scenarios,
/// it immediately allocates the first fragment to keep the `SplitVec` struct smaller.
///
/// # Examples
///
/// ```
/// use orx_split_vec::prelude::*;
///
/// // SplitVec<usize, Doubling>
/// let mut vec = SplitVec::with_doubling_growth();
///
/// assert_eq!(1, vec.fragments().len());
/// assert_eq!(Some(4), vec.fragments().first().map(|f| f.capacity()));
/// assert_eq!(Some(0), vec.fragments().first().map(|f| f.len()));
///
/// // fill the first 5 fragments
/// let expected_fragment_capacities = vec![4, 8, 16, 32];
/// let num_items: usize = expected_fragment_capacities.iter().sum();
/// for i in 0..num_items {
///     vec.push(i);
/// }
///
/// assert_eq!(
///     expected_fragment_capacities,
///     vec.fragments()
///     .iter()
///     .map(|f| f.capacity())
///     .collect::<Vec<_>>()
/// );
/// assert_eq!(
///     expected_fragment_capacities,
///     vec.fragments().iter().map(|f| f.len()).collect::<Vec<_>>()
/// );
///
/// // create the 6-th fragment doubling the capacity
/// vec.push(42);
/// assert_eq!(
///     vec.fragments().len(),
///     expected_fragment_capacities.len() + 1
/// );
///
/// assert_eq!(vec.fragments().last().map(|f| f.capacity()), Some(32 * 2));
/// assert_eq!(vec.fragments().last().map(|f| f.len()), Some(1));
/// ```
#[derive(Debug, Default, Clone, PartialEq)]
pub struct Doubling;

impl Growth for Doubling {
    fn new_fragment_capacity<T>(&self, fragments: &[Fragment<T>]) -> usize {
        fragments.last().map(|f| f.capacity() * 2).unwrap_or(4)
    }

    #[inline(always)]
    fn get_fragment_and_inner_indices<T>(
        &self,
        vec_len: usize,
        _fragments: &[Fragment<T>],
        element_index: usize,
    ) -> Option<(usize, usize)> {
        if element_index < vec_len {
            let element_index_offset = element_index + FIRST_FRAGMENT_CAPACITY;
            let leading_zeros = usize::leading_zeros(element_index_offset) as usize;
            let f = OFFSET_FRAGMENT_IDX - leading_zeros;
            Some((f, element_index - CUMULATIVE_CAPACITIES[f]))
        } else {
            None
        }
    }
}

impl GrowthWithConstantTimeAccess for Doubling {
    fn get_fragment_and_inner_indices_unchecked(&self, element_index: usize) -> (usize, usize) {
        let element_index_offset = element_index + FIRST_FRAGMENT_CAPACITY;
        let leading_zeros = usize::leading_zeros(element_index_offset) as usize;
        let f = OFFSET_FRAGMENT_IDX - leading_zeros;
        (f, element_index - CUMULATIVE_CAPACITIES[f])
    }
}

impl<T> SplitVec<T, Doubling> {
    /// Strategy which allows to create a fragment with double the capacity
    /// of the prior fragment every time the split vector needs to expand.
    ///
    /// Assuming it is the common case compared to empty vector scenarios,
    /// it immediately allocates the first fragment to keep the `SplitVec` struct smaller.
    ///
    /// # Panics
    /// Panics if `first_fragment_capacity` is zero.
    ///
    /// # Examples
    ///
    /// ```
    /// use orx_split_vec::prelude::*;
    ///
    /// // SplitVec<usize, Doubling>
    /// let mut vec = SplitVec::with_doubling_growth();
    ///
    /// assert_eq!(1, vec.fragments().len());
    /// assert_eq!(Some(4), vec.fragments().first().map(|f| f.capacity()));
    /// assert_eq!(Some(0), vec.fragments().first().map(|f| f.len()));
    ///
    /// // fill the first 5 fragments
    /// let expected_fragment_capacities = vec![4, 8, 16, 32];
    /// let num_items: usize = expected_fragment_capacities.iter().sum();
    /// for i in 0..num_items {
    ///     vec.push(i);
    /// }
    ///
    /// assert_eq!(
    ///     expected_fragment_capacities,
    ///     vec.fragments()
    ///     .iter()
    ///     .map(|f| f.capacity())
    ///     .collect::<Vec<_>>()
    /// );
    /// assert_eq!(
    ///     expected_fragment_capacities,
    ///     vec.fragments().iter().map(|f| f.len()).collect::<Vec<_>>()
    /// );
    ///
    /// // create the 6-th fragment doubling the capacity
    /// vec.push(42);
    /// assert_eq!(
    ///     vec.fragments().len(),
    ///     expected_fragment_capacities.len() + 1
    /// );
    ///
    /// assert_eq!(vec.fragments().last().map(|f| f.capacity()), Some(32 * 2));
    /// assert_eq!(vec.fragments().last().map(|f| f.len()), Some(1));
    /// ```
    pub fn with_doubling_growth() -> Self {
        Self {
            fragments: vec![Fragment::new(FIRST_FRAGMENT_CAPACITY)],
            growth: Doubling,
            len: 0,
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn get_fragment_and_inner_indices_unchecked() {
        let growth = Doubling;

        assert_eq!((0, 0), growth.get_fragment_and_inner_indices_unchecked(0));
        assert_eq!((0, 1), growth.get_fragment_and_inner_indices_unchecked(1));
        assert_eq!((1, 0), growth.get_fragment_and_inner_indices_unchecked(4));
        assert_eq!((1, 5), growth.get_fragment_and_inner_indices_unchecked(9));
        assert_eq!((2, 0), growth.get_fragment_and_inner_indices_unchecked(12));
    }
}